Internal combustion engines, such as multi-cylinder diesel engines, typically include a crankshaft, a camshaft and a rocker arm shaft. The crankshaft is connected with a plurality of piston rods, which in turn are connected with a plurality of corresponding pistons. Reciprocating movement of the pistons within corresponding combustion cylinders causes rotation of the crankshaft.
The crankshaft is typically interconnected with the camshaft via a gear set and thereby rotatably drives the camshaft during operation. The camshaft includes a plurality of cams, with each cam being associated with an inlet valve, and an exhaust valve or a fuel injector valve. More particularly, the rocker arm shaft carries a plurality of rocker arms, with each rocker arm having a roller follower which engages a corresponding cam on the camshaft. Rotation of the camshaft causes oscillatory pivotal movement of the rocker arms about the rocker arm shaft.
A problem with a conventional internal combustion engine as described above is that the rocker arm shaft is rigidly and immovably carried by a housing. The rocker arms pivot through a relatively small pivoting angle about the stationary rocker arm shaft. The small angle through which the rocker arms pivot is not sufficient to allow the formation of a hydrodynamic oil film between the rocker arms and the rocker arm shaft. As a result, the friction between the rocker arms and the rocker arm shaft may be relatively high and the energy required to pivot the rocker arms is increased. This decreases the efficiency of the engine. Additionally, the increased friction may cause increased wear or spalling between the rocker arms and the rocker arm shaft.
It is known to oscillate a rocker arm shaft through a small rotational angle using a rack and pinion arrangement in order to change the eccentricity of the rocker arms relative to the rocker arm shaft. However, the rocker arm shaft does not continuously or fully rotate within the rocker ends. Such a slight pivotal movement is not sufficient to create a hydrodynamic oil film between the rocker arm shaft and the rocker arms, or to reduce friction or improve efficiency of the internal combustion engine. An example of an internal combustion engine including such a rocker arm shaft is disclosed in U.S. Pat. No. 5,111,781 (Kaku, et al).
The present invention is directed to overcoming one or more of the problems as set forth above.